This project is focused on physiologically critical functions of NF-kappaB proteins and their regulators in the context of specific biologic reactions in vivo. Regulators of interest include the classical inhibitory IkappaB proteins, the non-inhibitory IkappaB family protein Bcl-3, as well as proximal components of the numerous signaling pathways that lead to to activation of NF-kappaB. Research is based on the discovery of specific defects (especially of the immune system) in mice rendered deficient for various NF- kappaB proteins or their regulators. The ultimate goal is to identify critical molecular targets of the NF-kappaB factors in specific immune responses/diseases and to identify the essential signaling pathways that activate the factors in these situations. Previously we generated mice deficient in both NF-kappaB1 and NF-kappaB2. These double knockout mice are completely blocked in the development of mature osteoclasts and of mature B cells. We have determined in adoptive transfer experiments that the blocks in generation of mature B cells and mature osteoclasts are intrinsic to these cell lineages. B cell development in double knockout mice is blocked during an early transitional stage in spleen, resulting in a complete absence of recirculating mature B cells. The mutant B cells are intrinsically more apoptotic than their wild-type counterparts. We now show that introduction of Bcl-2 into these double-deficient B cells, either via a transgene or via lentivirus-mediated transduction of bone marrow cells rescues the developmental block and allows for further progression of B cells. However, these Bcl-2-rescued, mutant B cells still fail to fully mature phenotypically and functionally. Neither constitutive nor antigen-stimulated antibody production is restored. Thus NF-kappaB1,2 are required for survival and functional maturation of B cells. We have shown previously that one of the signals responsible for activation of NF-kappaB in early transitional B cells comes from the BAFF receptor, a member of the TNF receptor family. The ligand BAFF induces processing of NF-kappaB2 p100 to p52, which activates nuclear translocation of RelB/p52. NF-kappaB2 processing is also important in stromal cells of lymphoid organs in response the lymphotoxin beta receptor stimulation, where it contributes to development of follicular dendritic cell network, B cell follicles, germinal centers and lymph node formation. Mice deficient in the IkappaB-like regulator Bcl-3 have milder, but similar phenotypes. However, we now show that Bcl-3, NF-kappaB2 double knockouts have unexpected additional phenotypes, including a severe multiorgan inflammation. This indicates unexpected redundant activities of these two proteins. Finally we have discovered that lack of NF-kappaB2 also prevents obesity-induced insulin resistance in standard assays, a phenomenon that are presently characterizing in detail.